Question

QRS complex of a standard ECG represents
A. Excitation or depolarization of atria
B. Depolarization of ventricles
C. Repolarization of ventricles
D. None of the above

Answer 1

Hint: ECG stands for electrocardiography. It is the process of producing an electrocardiogram. The graph of the voltage versus time of the electrical activity of the heart is electrocardiogram. It is done with the help of electrodes which are placed on the skin. The ECG is done to detect the arrhythmias, coronary artery disease etc. one may need an ECG if suffering from chest pain, shortness of breath, heart palpitations and other signs.

Complete answer:
There are three main components of an ECG. The P wave represents the depolarization of the atria.
The QRS complex represents the depolarization of the ventricles.The T wave represents the repolarization of the ventricles.Each heart beat represents progression of the depolarization that starts with pacemaker cells in the sinoatrial node. It spreads through the atrium,passes through the atrioventricular node into the bundle of His and then to the purkinje fibers and spreads down to the left throughout the ventricles.This pattern of depolarization gives characteristic ECG tracing.The QRS complex is the main spike seen on an ECG line.Here Q wave is downward deflection which is followed by P wave. R wave is an upward deflection and S wave is a downward deflection.Normally the QRS interval is 0.08 to 0.10 seconds.

Hence the correct answer is option ‘B’ i.e, depolarization of ventricles.

Note:The duration, amplitude and the morphology of the QRS complex is helping in diagnosing the cardiac arrhythmias, myocardial infarction, conduction abnormalities and other diseases.